package com.gree.shyun.util;


import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
/**
 * 校验文件是否一致
 */
public class CheckFileConsistency {

        protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6','7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

        protected static MessageDigest messageDigest = null;
        static {
            try {
                messageDigest = MessageDigest.getInstance("MD5");
            } catch (NoSuchAlgorithmException nsaex) {
                System.err.println(CheckFileConsistency.class.getName()+"初始化失败，MessageDigest不支持MD5!");
                nsaex.printStackTrace();
            }
        }
        public static String getFileMD5String(File file) throws IOException {
            FileInputStream in = new FileInputStream(file);
            FileChannel ch = in.getChannel();
            //80000000 bytes   76MB
            int maxSize=80000000;

            long startPosition=0L;
            long step=file.length()/maxSize;

            if(step == 0){
                MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0,file.length());
                messageDigest.update(byteBuffer);
                return bufferToHex(messageDigest.digest());
            }

            for(int i=0;i<step;i++){
                MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, startPosition,maxSize);
                messageDigest.update(byteBuffer);
                startPosition+=maxSize;
            }

            if(startPosition==file.length()){
                return bufferToHex(messageDigest.digest());
            }

            MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, startPosition,file.length()-startPosition);
            messageDigest.update(byteBuffer);


            return bufferToHex(messageDigest.digest());
        }

        public static String getMD5String(String s) {
            return getMD5String(s.getBytes());
        }

        public static String getMD5String(byte[] bytes) {
            messageDigest.update(bytes);
            return bufferToHex(messageDigest.digest());
        }

        private static String bufferToHex(byte bytes[]) {
            return bufferToHex(bytes, 0, bytes.length);
        }

        private static String bufferToHex(byte bytes[], int m, int n) {
            StringBuffer stringbuffer = new StringBuffer(2 * n);
            int k = m + n;
            for (int l = m; l < k; l++) {
                appendHexPair(bytes[l], stringbuffer);
            }
            return stringbuffer.toString();
        }

        private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
            char c0 = hexDigits[(bt & 0xf0) >> 4];
            char c1 = hexDigits[bt & 0xf];
            stringbuffer.append(c0);
            stringbuffer.append(c1);
        }

        public static boolean checkPassword(String password, String md5PwdStr) {
            String s = getMD5String(password);
            return s.equals(md5PwdStr);
        }
}
